1. Field of the Invention
This invention relates to fast-setting magnesium phosphate cements. More particularly, it relates to improved fast-setting magnesium phosphate cements containing an effective amount of fiber to increase the impact strength of the resulting concrete.
2. Related Art
Cementitious compositions having a very fast setting time and prepared by mixing a magnesium-containing component with an ammonium phosphate component and an optional aggregate are popular for use in repairing or patching cracks, holes and spalled areas of highways, airfield pavements and bridge decks, as well as for a variety of commercial and industrial applications.
U.S. Pat. No. 3,879,209 (Limes et al., Apr. 22, 1975) discloses a process for making such a fast-setting concrete comprising establishing a mixture of an aggregate, containing at least 10 percent by weight of magnesia, and ammonium phosphates in aqueous solution. This patent discloses that a commercial agricultural fertilizer product known as sequestered phosphatic solution (SPS) is particularly suitable as a source of the ammonium phosphate. This reference is one of many references which disclose a class of magnesium phosphate fast-setting cementitious compositions which when mixed with an aqueous component sets at ambient temperatures in substantially less than one-half hour after mixing. The strength development of these compositions is sufficiently rapid to permit, e.g. automobile traffic thereover, within a few hours following application. Additionally, these compositions exhibit excellent adhesion to various substrates, e.g. Portland cement concrete and steel, and they attain high compressive strength and are quite durable.
U.S. Pat. No. 2,522,548 (Streicher, Sept. 19, 1950) discloses the preparation of phosphate gel binders by reacting metal oxides, e.g. magnesium oxide, and primary phosphate solutions. These binders can contain a filler, e.g. kieselguhr. However, this reference is directed to the use of these phosphate gel binders in a refractory application and further states that the primary ammonium phosphate is not effective in its process.
U.S. Pat. No. 3,475,188 (Woodhouse, Oct. 28, 1969) discloses a refractory composition comprising a liquid bonding agent, for example sequestered phosphatic solution, that is diammonium phosphate and polyphosphate, absorbed onto an absorbent, for example quartzite, and a particulate refractory substance containing MgO. This reference further states that phosphoric acid and magnesia resulted in relatively low strength chemically bonded composition due to their rapid reaction. Again, this reference is directed to refractory compositions and does not disclose the process of the present invention.
U.S. patent application Ser. No. 617,317, filed June 7, 1984, which is a continuation-in-part of U.S. patent application Ser. No. 522,077, filed Aug. 11, 1983 and now abandoned, and EPC patent application 84201155.3, published Mar. 6, 1985, discloses a particularly effective solid phosphorus pentoxide material suitable for use in these fast-setting magnesium phosphate cements. This material is prepared by a process which comprises mixing a porous material with a liquid phosphorus pentoxide material and heating the mixture until a dry solid is produced. This solid phosphorus pentoxide material can then be dry blended with a solid component comprising magnesium oxide, magnesium hydroxide, magnesium carbonate or mixtures thereof. When hydrated, this dry blend has been found particularly advantageous in the fast-setting magnesium phosphate cement applications described above. This reference discloses that an aggregate including fibers can be added to the cement to enhance its strength, however the significant impact strength increase disclosed by this invention was not anticipated.
U.S. Pat. No. 3,960,580 (Stierli et al., June 1, 1976) discloses magnesium phosphate concretes containing specified oxy-boron compounds such as sodium borate as set retarders. The phosphate component of the cementitious compositions disclosed by Stierli et al. appears to contemplate either a dry solid monoammonium phosphate component, or a solid monoammonium phosphate component comprising a mixture of monoammonium phosphate and another solid phosphate selected from diammonium phosphate and sodium pyrophosphate. A solid activator component comprising a P.sub.2 O.sub.5 material absorbed onto a porous material is not contemplated or disclosed.
U.S. Pat. No. 3,752,684 (Kiehl et al., Aug. 14, 1973) discloses an insulating refractory material containing magnesium phosphate, alkaline earth oxides, silica and mineral fibers. The fibers are typically mineral wool or asbestos fibers. This reference does not disclose the improved fast-setting magnesium phosphate cements containing fiber as disclosed in this invention.
U.S. Pat. No. 4,417,925 (Cherry, Nov. 29, 1983) discloses a ceramic fiber refractory mixture. This mixture typically contains ceramic fiber, aluminum phosphate powder, calcine magnesia, water soluble binder, organic polymer plasticizing agent and an acidifying agent. The preferred ceramic fibers are selected from the group consisting of aluminum fibers, aluminum silicate fibers, chrome-containing fibers and mixtures thereof with fibers of aluminum silicate being the most preferred of the group. Again, this reference does not disclose the improved fast-setting magnesium phosphate cements containing fiber of this invention.
U.S. Pat. No. 84,293 (Norton, Mar. 12, 1907) discloses the preparation of refractory materials by combining asbestos fiber and magnesium oxide with water under pressure. This reference does not disclose the improved fast-setting magnesium phosphate cements containing fiber of this invention.